Method of resisting radiation damage to organic fluids and compositions therefor



Unit State P m Q METHOD OF RESISTING RADIATION DAMAGE TO ORGANIQ FLUIDSAND COMPOSITIONS THEREFOR Robert 0. Bolt, San Rafael, and James G.Carroll, Martinez, Califi, assignors, by mesne assignments, to theUnited States of America as represented by the United States AtomicEnergy Commission No Drawing. Filed June 29, 1956, Ser. No. 595,014

12 Claims. (Cl. 252-28) The present invention relates in general toconducting operations involving fluid organic substances undercircumstances wherein those substances are subjected to nuclearradiation. More particularly the invention relates to an improved methodfor resisting damage to said fluid organic substances induced by nuclearradiation, and to improved compositions of fluid organic substanceswhich compositions are resistant to deterioration in the presence ofnuclear radiation.

The derivation of useful nuclear power will often require the use, in anintensely radioactive environment of a reactor, of compositions of fluidorganic compounds for functions dependent primarily on fluidity. Suchcompositions include especially lubricants as Well as power transmissionfluids and the like. However, as a general rule, nuclear radiationdeleteriously reduces the fluidity of organic compounds, often to theextent of complete solidification in a short time. This is notable inthe case of liquid hydrocarbons which include, to a large measure, thevariety of liquids normally adapted to serve as efficacious lubricantsand other such functional liquids in nonradioactive environments. Forexample, a representative conventional commercial petroleum hydrocarbonlubricating oili.e., paraflinic, solvent-refined Western (United States)automotive oil, SAE-30upon irradiation for four weeks in a reactor,thickened from its original viscosity range of medium-weight automotiveoil to virtually a solid. In such instance the approximate cumulative ofradiation dosage sustained amounted to about 1.7 slow neutrons persquare centimeter and a proportionate dosage of gamma radiation and fastneutrons. This represents an exposure which is considered moderate inapplications of organic materials around mobile reactors.

As a matter of definition the reactor radiation dosages herein areexpressed as slow neutrons per square centimeter. This term is usedbecause slow neutrons are easily measured and not because such neutronsare the most damaging to organic fluids. Indeed, the fast neutrons andgamma components of reactor flux cause more damage than slow ne'utrons.In graphite-moderated reactors, such as exist at Oak Ridge andBrookhaven National Laboratories, the fast neutron (above about 1 mev.in energy) and gamma (1 mev. average energy) components of radiationflux are present to the extent of about and 50% respectively of themeasured slow neutron component. Such slow neutrons are typicallymeasured by the activation of cobalt. More explicitly, in accordancewith conventional practice for measuring neutron dosages cobalt orcobalt-aluminum alloy monitors are exposed both alone and covered with acadmiumshield. The subtraction of the activity of the shielded monitorfrom the activity of the unshielded monitor yields data from which theslow neutron dosages can be 2,967,827 Patented Jan. l0

calculated. The dosage values used herein were obtained in such amanner.

As indicated above, the loss of fluidity due to nuclear radiation incompositions of fluid organic substances has imposed a serious obstacleto the successful design and utilization of nuclear power plants. Thiseffect tends to fluid organic substances which are useful in radioactiveenvironments without the early replacement heretofore required for suchcompositions. A further object is to provide improved lubricantcompositions which are resistant to damage due to nuclear radiation. Astill further object is to provide a constant viscosity lubricantcomposition having a low rate of change in viscosity with exposure tonuclear radiation. Additional objects will become apparent from thefollowing description of the invention.

In accordance with the present invention, the foregoing objects areattained by the use of compositions comprising fluid organic substancesin combination with certain styrene polymers. We have discovered thatthe addition of these styrene polymers to fluid organic substancesincreases the viscosity and improves the nuclear radiation resistance ofthe resulting composition. Heretofore it has been proposed to add highmolecular Weight polymers to lubricating oils to improve theviscosity-temperature relae tionship of said lubricating oils. Suchso-called viscosity index improvers include ester polymers, polyalkenes,polyesters and polystyrene-alkene copolymers. As distinguished from suchcompounds which improve the V.I. of lubricating oils, the lower alkylstyrene polymers of the present invention do not improve appreciably theV1. of lubricating oils.

Applicants have discovered that the lower alkyl styrene polymers such aspoly (alpha-methyl styrene) effectively thicken various base oils andimpart to the mixture nuclear radiation resistance, as measured byviscosity increase, superior to other thickeners. Upon incorporating aslittle as only a few percent of these oil soluble alkyl styrene polymersinto an organic liquid base oil, the degree of radiation-inducedviscosity increase resulting from a given dosage of nuclear radiation ismarkedly reduced, the rate of progressive thickening under a givenintensity of continuous nuclear reactor radiation is substantiallydecreased and inhibited, and otherwise a ro. nounced relative resistanceto nuclear radiation thickening-is imparted to the base oil. Theparticular structure of the styrene polymers with their highpercentageof aromatic rings apparently permit a high degree of reso-loccur in the presence of oxidation inhibitors, inhibitors of freeradical reactions, metal deactivators and viscosity index improvers,various combinations of which yield preferred' embodiments of theinvention as described more, fully hereinbelow. Furthermore, thepresence of -the" a poly (alkyl styrene) in admixture with the base'oildoes" not materially detract from the lubricating efiiciency of the baseoils to which it is added, and such mixtures of the desired lubricatingoil viscosity range even with relatively large proportions of the liquidpolymerization products of lower alkyl styrenes yield satisfactorylubricants. Hence, utilizing such mixtures, the present inventionprovides an improved method for the lubrication of systems beingsubjected to nuclear radiations normally deleterious to lubricants.Being of such efiiciency and having such beneficial attributes, thepresent method clearly affords substantial practical advantages in theapplications of functional fluids in nuclear power plants and the like.

The oil soluble styrene polymers employed in the present invention arepolymers of styrene substituted such as in the alpha position with loweralkyl groups, which substitution is believed to decrease the activity ofthe double bond sufficiently in the manner to produce low molecularweight oil-soluble polymers. Preferably the polymers are liquids such asa-methyl styrene polymer which is miscible with oils includinglubricating oil.

Hence, the lower molecular weight alpha-alkyl styrenes with a minimum ofaliphatic carbons are the preferred monomers and the polymers ofa-methyl styrene are especially preferred. Other substituted styrenesfrom which polymers may be formed are para-methyl styrene,alpha-methyl-para-methyl styrene, para-isopropyl styrene, unsymmetricalmethyl para-tolyl ethylene, unsymmetrical methyl para-cumyl ethylene andthe like. Various ways of preparing the monomers and the polymerstherefrom are disclosed in ACS Monograph No. 115, entitled Styrene, ItsPolymers, Copolymers and Derivatives," by Boundy and Boyer (Reinhold PubCorp., 1952), and in US. Patent 2,215,569. Suitable liquid tit-methylstyrene polymers are obtained from Dow Chemical Co., as Dow Resins276-V2 and V9, which have viscosities at 60 C. of 100-200 and 700-1000cps., respectively; these are believed to be, or contain mostly, higherpolymers than dimers which distills at 158-l60 C., under 10 mm. Hgpressure, according to US. Patent 2,227,808.

The lower alkyl styrene polymers employed are normally those which aresufficiently viscous to thicken substantially the base oil used.Suitable polymers usually have viscosities from 100 cps. to very highviscosities so long as the polymer is miscible with the base oil. Fromthe standpoint of vaporization losses the higher boiling products ofpolymerizing lower alkyl styrenes which contain only minor amounts ofmaterials of appreciable volatility at operating temperatures arepreferred. A 5% boiling point of 300 F. would be a minimum, althoughpreferably the 5% boiling point should be above 500 F. For example, asuitable poly (oz-methyl styrene) has a 5% to 90% boiling range of150-300" C. at 5 mm. Hg. Since the lower alkyl styrene polymerizationproducts do not crystallize upon cooling but rather form glasses, theyare superior, from the pour point standpoint in lubricant compositions,to other aromatic materials which crystallize upon cooling.

The lower alkyl styrene polymers are used in sufiicient amount at leastto thicken substantially the base oil. The mixture of polymer and baseoil may contain from 1 to 70% of the polymers, although usually to 40%results in a satisfactory lubricant.

In the mixture of base oil and alkyl styrene polymer, the base oil canbe petroleum-derived hydrocarbon fractions of suitable viscosity rangesfor the desired service. Representative of the better of these are thecommercial, parafiinic, solvent-refined lubricating oils derived fromWestern (United States) petroleum, and also from Pennsylvania, MiddleEast, Mid-Continent (United States) and Coastal (United States)petroleum crudes, of the various common viscosities ranging from lightturbine oil (e.g., 150 neutral), hydraulic fluids, and includingautomotive oil (e.g., SAE-30), and on through heavy steam cylinder, gearand chain oils. However, the so-called synthetic lubricating oils aregenerally preferred in view of their usually superior response toimprovement by additives for oxidation inhibition and radiationresistance. These include the alkyl aromatics, organic esters anddiesters and polyesters, which have viscosities within much the sameranges as the foregoing petroleum hydrocarbon liquids and alsopreferably have 5% boiling points above 500 F. The alkyl aromatics areexemplified by technical mixtures of alkylbenzenes of molecular weightsapproximately of the order of 250 to 400, derived as byproducthigh-molecular-weight bottoms in detergent alkylbenzene manufacture.

Also practically applicable are various liquid individual organichydrocarbon compounds, especially long-chain parafilns andlong-chain-parafiin-substituted aromatics, typified by octadecylbenzene:

CrsHsr which approximates the viscosity of textile spindle oil,amylbiphenyl, also approximating the viscosity of textile spindle oil,hexadecane (i.e., cetane), which approximates the consistency of lightinstrument oil, and polyamylnaphthalenes. Among the esters, differentspecies afiording appropriate viscosity, heat resistance qualities, andthe like, and thus adapted to functional service, are likewise varied.Prominent, though, are those derived from dicarboxylic acids botharomatic and aliphatic, in conjunction with aliphatic, or, better,straight-chain saturated aliphatic, alcohols, and especially from thoseacids and alcohols of such types respectively comprising from about sixto twelve carbon atoms in their molecules. Such compounds provide aliberal assortment of diflerent viscosities and other functionalproperties; representative of these are: di(Z-ethyl hexyl)sebacate,i.e.,

approximating the consistency of light turbine oil and instrument oil;didecyl terephthalate, i.e.,

approximating the consistency of automotive oil; and di(Z-ethyl-hexyl)ortho phthalate.

Since the alkylbenzenes and organic esters are not commerciallyavailable generally in all lubricating oil viscosities, thepolymerization products of lower alkyl styrene are especially desirablefrom a practical standpoint for use in combination with the lowerviscosity alkylbenzenes and organic esters. As examples of thisparticular aspect of the invention, poly (a-methylstyrene) may becombined in a ratio of 30 parts to 70 parts of an alkyl benzene mixturewith a viscosity of a furnace oil to produce a material with a viscosityin the SAE 10W crankcase oil range. Similarly poly (a-methylstyrene) maybe combined in the ratio of 35 parts to 65 parts of di-2-ethylhexylsebacate, which has aviscosity of a light hydraulic oil, to produce alubricant of an SAE W crankcase ,oil viscosity.

While the presence of the lower alkylstyrene polymers in admixture withthe base oil results in a substantial reduction in the tendency of theoil composition to increase in viscosity upon exposure to nuclearradiation, the viscosity of the mixture increases upon continuedexposure to nuclear radiation. As indicated hereinabove, a specialaspect of the present invention is concerned with the use of a thirdcomponent to effect a further improvement in the resistance of thecomposition to viscosity change from exposure to nuclear radiation. Forthis purpose, there is added to the mixture of alkylstyrene polymer andbase oil, which mixture tends to increase in viscosity with exposure tonuclear radiation, a minor amount of a polymeric material which tends todecrease in viscosity with exposure to nuclear radiation. Compositionsof substantially constant viscosity in radioactive atmosphere areobtained by the addition of such polymeric material in an amountsufiicient to offset substantially the thickening effect due to theviscosity increase of the mixture of base oil and lower alkylstyrenepolymer. Where the two efiects do not exactly compensate each other, thetwo effects are compensating in a substantial amount and hence thecomposition is improved with respect to viscosity changes due toradiation effects. The radiation-induced viscosity-decreasing polymericmaterials are usually viscosity index improvers and hence theviscosity-temperature characteristics of the resulting proceeding togreater cumulative radiation dosages, the" viscosity will ultimatelycommence to increase at about the same rate per unit dosage as with noradiation} induced viscosity-decreasing polymeric material present. Formany functional services, the desired duration of usefulness of the oilcomposition'will not extend beyond the period of decreased or constantviscosity. Thus, the resulting compositions are radiation resistant andin the proper viscosity range are useful as lubricants, insulating thehigher molecular weight oil-soluble liquidgpolymers of olefins,v e.g.,propylene or butylene, but preferablyiso- The radiation-inducedviscosity-decreasing polymeric I material is, as indicated above,employed in small amounts generally ranging from about 2-3 %1 up to.about 15-20%. 5

Instead of the above viscosity improving polymeric materials, polyethersmay be incorporated as all or part of the radiation-inducedviscosity-decreasing component of the composition. In some instances thepolyethers may desirably replace all or part of the base oil componentin the mixture of base oil and lower alkyl styrene polymer. Thepolyether liquids'suitable for service in radioactive atmosphere includefluids containing at least 3 ether linkages in the molecule. Thepolyether molecule preferably contains a multiplicity of ether linkagesspaced between short, saturated and straight or branched chain aliphaticradicals. Furthermore, the fluid employed should have a viscosityappropriate, in combination with the other components, for theparticular service for which the composition is to be used. The mostsuitable polyethers will have molecular weights ranging from about 400to 3000 or above. As examples may be mentioned polymers of propeneoxides, e.g., 1,2-pr0pene oxide, wherein the polymerization may beinitiated with aliphatic or arylmonohydric alcohols or esters, and theremaining terminal hydroxy groups of the polymer may be esterified oretherified. Suitable polyethers are further Viscosity Increase ofOrganic Fluids, in the names of G. H. Denison, F. A. Christiansen, R. 0.Bolt and J. W.

Kent. A furth'er advantages of the polyethers is that nuclear radiationenhances the antiwear, antiseizure and general lubricity qualities ofthe polyethers.

Theradiationdamage can usually be further improved by blanketingthe oilcompositions with inert gases such as nitrogen, helium and the like. Insuch instance where oils, hydraulic fluids, gear lubricants, dashpotoils, scien- 1 tific instrument lubricants, shock absorber oils and thelike which exhibit relatively little change in viscosity with exposureto nuclear radiation.

The polymeric materials exhibiting the tendency to decrease in viscosityupon irradiation include the following viscosity-improving-polymers':polymerized acrylate esters such as the polymer of alkyl methacrylate,e.g., didodecyl methacrylate (as disclosed more fully in applicationSerial No. 380,146, filed September 8, 1953, now abandoned, for a Methodof Inhibiting Irradiation- Induced' Viscosity Increase or OrganicFluids, in the names of F. A. Christiansen, R. 0. Bolt, J. W. Kent andG. H. Denison) examples of other suitable acrylate ester polymers arethe oil-soluble polymers of isobutyl acrylate, octyl acrylate, cetylacrylate, amyl methacrylate, nand iso-hexyl methacrylates, and the like,and the oil-soluble copolymers of two or more of such acrylates andmethacry-lates. Likewise suitable are the copolymers of styrene andolefins, e.g., isobutylene, such as referred to at page 874 et. seq. ofACS Monograph No. 115, Styrene, Its Polymers, Copolymers andDerivatives, by Boundy and Boyer (Reinhold Publ. Corp., 1952), or asreferred to in US. Patent 2,421,082, or as marketed by Monsanto ChemicalCorp., under the trade name Santodex. Also,

oxygen is excluded, a still further improvement in resistancetoradiation damage can sometimes be obtained by employing the branchedchain species rather than the. v straight chain' alkyl groups, wherethey appear in the materials refer-redto above. v

The presence of, other additives incorporated in the mixture .of base.oil and lower alkyl styrene polymer, with or without viscosity indeximprovers, are normally unobjectionable, unless they adversely reactwith components of the mixture or are themselves undesirable in anuclear radiation environment. These additives, in their own variousspecific manners, enhance the value of the compositions and consequentlytend to complement the lower alkyl styrene polymers in improving theoverall efiiciency of the resulting compounded oil.- Fof'example, it maysometimes be desirable to incorporate in the oil composition smallamounts of antioxidants, of

which are preferred the organo selenides such as the dialkyl and diarylmonoselenides (as disclosed in application Serial No. 380,144, filedSeptember 8, 1953, inthe names of F. A. Christiansen, J. W. Kent, R. 0,Bolt' 7 and G. H. Denison, for a Method of Inhibiting Radiation Damageto Organic Fluids. Especially in the presence of metals, e.g., iron,copper or silver, the oil com-' v zothiazole, to aid in inhibiting theadverse thickening of. p the oil composition in services involvingexposure. to

nuclear radiation. Sometimes also desirable are inhibitors of freeradical reactions (i.e., scavengers for free radicals), which inhibitorsare preferably iodo-substituted aromatic compounds such as iodobenzene,iodonaphthalene, iodobiphenyl and like compounds, as disclosed inapplication Serial No. 380,147, filed September 8, 1953, in the names ofR. 0. Bolt, J. G. Carroll, J. W. Kent, F. A. Christiansen and G. H.Denison, for a Method of Inhibiting Irradiation Induced ViscosityIncrease of Organic Fluids.

These secondary additives, namely, the oxidation in hibitors, metaldeactivators and free radical scavengers are generally employed in smallamounts such as 0.0051% to 5l0%, by Weight of the oil composition.

In the following examples, the viscosity change is employed as theprimary criterion of determination. The index of damage, 1 (or 1 isdefined as the viscosity of an irradiated fluid at the temperature, T(or T at which the viscosity of the starting material was one centistoke(cs.) (or 10 cs.). This index provides a common comparative basis forfluids of widely difiering vis- 5 use and a solution of the polymer intoluene having a viscosity of cs. at 20 C. The polybutene had a 210 F.viscosity of 120,000 cs. The styrene-olefin copolymer is derived fromstyrene and olefins of 8-12 carbon atoms and had viscosities of 12,000S.S.U. at

10 100 F. and 1410 at 210 F., a gravity of 26.6 API and a flash point of350 F. Samples of the fluids made up of the base oil plus the indicatedamounts of the additives were placed in 1020 steel containers, open tothe air, and exposed at 25 C. to various dosages of Co 15 gamma raysfrom a 600-curie source of the Brookhaven tube type (see Nucleonics,vol. 9, pp. 10-13 [1950]), which gives a flux of 1.69 X 10 r./hr. or4.06 X 10 r./day. The amounts (in percent by weight of the composition)of the several additives and the results of the 20 irradiation are shownin the following Table I:

Table I Test No. Additive Exposure Viscosity Amount, (Centistokes)percent Days RXIO at100 F. at 210 F.

Poly (a-methylstyrene) cosities. By this means the initial viscosity ofeach fluid begins at one es; and viscosity change can be measured interms of deviation from this common point.

The following examples further illustrate the compositions and methodsof the present invention:

EXAMPLE I A series of fluids of lubricating oil viscosity were preparedwith the additives of the present invention and also other additives forcomparison, as shown in Table I. The base oil (denoted here as A todistinguish from other base oils in other examples) was composed ofmixed alkylbenzenes with an average molecular weight of about 250 andwere mainly monoalkylbenzenes, wherein the alkyl group was derived frompropene polymers. In the alkylbenzene base oil was included 5% dodecylselenide and about 0.1% quinizarin. The poly (ix-methyl styrene)employed was obtained as Dow Resins 276-V9 from Dow Chemical Co., andhad a viscosity at 60 C. of 700-1000 cps., and a 5% to 90% boiling rangeof EXAMPLE II Another series of fluids with various base oils andadditives were placed in Pyrex vessels, open to the air, and exposed at25 C. to the same source and flux as in Example I. Base oil B wascomposed of mixed alkylbenzenes of an average molecular weight of 250and were mainly monoalkyl benzenes wherein the alkyl group was derivedfrom propene polymer. Base oil C was a poly (propene oxide) of about1000 molecular weight and having phenyl and methyl ether groups at theends of the propene oxide polymer chain, the polymer oil had viscositiesof 62.5 and 10.7 at 100 F. and 210 F., respectively. Base oil D wasdi(Z-ethylhexyl) sebacate.

0 Each of these base oils B, C and D contained 5% didoirradiations aregiven in the following Table II.

Table II Exposure Viscosity (Centl- Index of Damage Base stokes) TestNo. Oil Additive Amtz,t TV a F percen 10 mo Days 13x10 at 100 F. at 210F.

I Poly (a-methylstyrene) 30 Y B l i z lgg g 3; 5 0 27.4 4.4 150 10.0

0y a-me y yreue 30 B 38 11.02 0.45 20.5 4.29 150 9.7

o.y a-me y -yrene B gq z fi l g i 5 40.92 1.00 24. 3 4. 01 150 9.0

0 y a-me y s yrene B {g g t ii l g g 53 03 01 2.73 23.3 3.93 150 3.3

0 y a-me ys yrene B {g i i ig gz g &8 103.30 4. 40 v 23.9 3 34 150 3.7

I o y a-IIIB y yrene B lstyrenemefin copolymet 5 139.10 5. 05 24.0 3.30150 3.3 C Poly (a-methylstyrene) 30 0 0 95.1 11.5 221 10.0 0 d5 30 11.020.45 95. 7 11.2 221 9. 9 o 30 40. 90 1. 00 93. 3 11.1 221 9. 3 o 30 03.01 2. 73 93. 0 10. 9 r 221 9. 5 o 30 103. 30 4. 40 109 11. 2 221 10. 0 o30 139. 10 5. 05 115 11.5 221 10. 0 E 2 0 0 59.0 1 11.9 227 10.0 E 211.02 0.45 54.7 9. 74 227 3.2 E 2 20.93 0. 54.2 9.51 227 3.0 E 2 40.70 1. 00 53.3 9.43 227 7.3 E 2 01.73 I 2.53 53.5 9.19 227 7.7 E 2 103.304.40 01.0 3.94 227 7.4 D- I 0 5 0 12.5 3. 31 114 10.0 20.93 0. 35 13. 53; 49 114 10. 7 40. 90 1. 00 15. 1' 3. 74 114 12. 0 30 03. 01 2. 73 10.43. 97 114 13. 0 53g 0 0 30.2 0.23 172 10.0 l g z i l? i t f kg 11.0 0.4535.4 0.03 172 9 3 0y ame ysyreue %t; re1 10-51e1 1 (iogolymfr) 33 40.901.00 35.0 5.93 172 9.0

o ya-me y s yrene 5 g i z ,i t 38 03.01 2.73 35.0 5.91 172 0.0

o y a-me y s yrene {styrene o1efin copolymer) 5 103.30 4.40 37.4 0.14 I172 10.0 32330163230113- 3 n3 .3 32 332 3; 33 2 40: 90 1: 00 1713 4119127 11: 2 2 03. 01 2. 73 13.4 4. 40 127 11.5 D 2 103. 30 4. 40 22. 1 4.34 127 13.4 D 2 139.10 5.05 27.7 7.13 127 13.3 1) 2 0 0 22. 7 5. 33 I153 10. 0 D 2 11.02 0. 15.7 3. 95 153 0.3 D 2 20. 93 0. 35 15. 7 3. 93153 0. 7 D 2 40.70 1. 00 10.9 4.01 153 1 7:0- 1) 2 01.73 2. 53 17.3 4.22153: 7.2 D 2 103.30 4. 40 23.1 4.99 153 9.0' D 2- 139. 10 5. 05 31. 2 7.07 153 13. 5: 1) 30 0 0 25. 0 4. 57 150 10. 0 D 30 43. 91 1. 99 20. 0 4.09 150 10. 3 1) 30 79.05 3.24 29.3 5.07 150 11.4

EXAMPLE III Various fluids thickened to difiering consistencies withpolybutene were made up and tested as indicated in the test No. 79 therewas also-5% ofa pinene-P S reaction following Table III. Therein thepoly (a-methylstyrene) product, obtained as Santolube 394C" from=Monsanto and polybutene are as described in more detail in Ex- ChemicalCorporation. 4

that in the composition for test No. 74 the amount of Table 111 TestNos.

Base 1 111104 74.05 00.20 50.95 5 4 Base 1 11111113 1 v 03.95 55.9543.95 2.95 27.95 P51 01- ethylstyrene) 15.00 21.30 33.0 13.00 32.0040.00 35.00 49.00 Polybutene 5.50 7.00 11.0 3.00 7.00 11.00 12.00 13.00Viscosities (03.):

ample I, except that the polybutene used in test No. 80 EXAMPLE IV had a210 F. viscosity of 18,000 centistokes. Base oil A was the same as usedin Example 1. Base oil F Some of the test oils from Example III,identified as didodecyl'selenide was 4.95% and in the composition for isan alkyl benzene mixture of an average molecular weight of about 330-340and consisting largely of dialkyl benzenes with the para isomerpredominating (as derived as by product high molecular weight bottoms indetergent alkylbenzene manufacture from alkylation of benzene withpropene polymer). Both the base oils A and F contest oil III-74, etc.,.and others asindicated below were top and exposed to radiation from asource having an average gamma energy of about I mev. and consisting ofasurrounding array of discharged enriched uranium 1 fuel elements from acanallgamma reactor. 13110131 0000 tained 5% didodecyl selenide and 0.50quinizarin; except 75 ties at F. and 210 F. weremeasured-before' radia-t11 tion and after varying radiation exposures. Test oil IV- 81 wascomposed of 67.2% of the 250 molecular weight alkylbenzene mixture ofbase oil A, 21.8% of the poly (a-methylstyrene) described in Example I,5.98% of the styrene-olefin copolymerdescribed in Example I, 4.97% ofdidodecyl selenide and 0.05% quinizarin. Test oil IV-83 was composed of45.95% of the 330-340 alkylbenzene mixture of base oil F, 40% of thesame poly (a-methylstyrene), 9% of the styrene-olefin copolymer,

compositions, their viscosities and results of four-ball wear tests aregiven in following Table V. The wear test is carried out by rotating 3one-half inch steel ball at 775 r.p.m. for 30 minutes against threestationary balls (steel or bronze as indicated) which are covered withthe test lubricant. A load of 10 or 20 (as indicated) kilograms isapplied vertically during the test. The wear scar areas formed on thethree stationary balls are measured at the end of the test.

Table V Test Nos.

Composition (percent by wt.):

Base 011A 76. 45 51.95 Base 011 F 54. 45 44. 95 41. 45 27. 95 32. 95 48.95 Base Oil G 54. 45 Petroleum Bright Stock 10 Poly (a-MB styrene) 15 3332 35 32 33 49 51 30 Styrene-Olefin Copolymern 3. 8. 5 11. 5 7. 5 18 118 Vinyl ether resi 13 Viscosity (SSU):

100 F 0 291 767 1, 394 1, 402 1, 570 3, 257 3, B60 6, 530 0 148 298 529504 517 1,065 1, 080 2,180 5 56. 2 71. 8 111 101 89. 8 175 145 358Viscos ty Index 2 124 79 101 86 48 95 51 112 Viscos1ty (08.):

210 F 3. 37 9.12 13.4 23.0 20. 7 18.0 37. 3 30. 7 77.0 Wear (mm.):

Steel 011 Steel (10 kg.) 0. 57 0. 54 0. 52 0. 51 0.44 Steel on Steelkg.) 0.60 0.47 0. 52 Steel on Bronze (10 kg.) 1. 22 1. 57 1. 55 0. 86 O.54

n 0.05 a o uinizarin. Test 5% of d1dodecyl selenide a d 7 f q EXAMPLE VIoil IV-86 was composed of 71.59% of the 330-340 alkylbenzene mixture,18% of the poly (a-methylstyrene), 5% of the styrene-olefin copolymer,5% of the didodecyl For comparison with the results in Table V, thefollowing wear data were obtained on conventional maselenide and 0.05%quinizarin. The data are given in terials; silicone 200 is thepolymethyl silicone marketed following Table IV.

by Dow Corning as DC. Silicone 200.

Table IV Viscosities (ca) Alter Radiation to Before irradia- Test N0.Fluid tiou 5x10 R 10 B. 5X10 R 100F 210F 100 F. 210 F. 100 F. 210F. 100F. 210 F.

EXAMPLE V Table VI A series of fluids of varying viscosities wereprepared from base oils A and F, heretofore described, and base WearScar (mm.) oil G which was an alkylbenezene mixture similar to base oilF but with an average molecular weight of about ter l Steel on SteelSgeell on 380. All the base oils were combined with 5% didodecylselenide and 0.05% quinizarin. To these base oils were 10 kg. 20 kg. 10kg. added varying amounts of the poly (a-methylstyrene) andstyrene-olefin copolymer heretofore dtilscr bed. {ks SAE 30 Mom on 0.24030 L20 lndlcated below, a petroleum bnght stock av1ng a v1s- SAE GearQ34 0,87 cosity of 210 SSU at 210 F. was used 1n one fiuid and511010116290 8 the vinyl butyl ether resin, described hereinbefore. The

I EXAMPLE VII quinizarin and the remainder the 330-340 molecular Thetest oils set forth in Table V above and-hereinweight mixedalkylbenzenes of base oil F' used in Ex after identified as test oilV-88, etc., were subjected at ample III there were added various gellingagents to form. 25 C. to gamma radiation as indicated below, at variousgrease compositions. The following Table VIII shows dosages in Pyrexglass containers open to the air and the amount of gelling agents andother added agents in in closed magnesium containers under oneatmosphere of the final composition. Therein, the estersil was anhyhelium, substantially air-free. The fiuids' in glass containers (tests97-104) were exposed to the source used Pont de Nemours & Co. under thename Du Pont Silica in Example I and the samples in the magnesium con-GS-199S (see also Patent 2,752,310, column 2, lines tainers (tests105-414) were exposed to the source used 40-41); the carbon black wasAcetylene Black from in Example IV. The fluid identified as VII114 wasShawinigan Products Corp; the graphite was Ache-soncomposed of 30% ofthe poly (ot-methylstyrene) and 39 Graphite" from Acheson CarbonCompany; the the remainder a eutectic of about 23 biplienyl andmolybdenum disulfide was Molykote from Alpha Corp., 77% diphenyl oxide,marketed as Dowtherm A by Greenwich, Connecticut; and the laurylphosphoric acid Dow Chemical Co. The results are given in the follow- 15was a mixture of monoand di-lauryl phosphoric acids ing Table VII.obtained as Ortholeum-162 from the Du Pont Corn- T able VII Viscosities(cs. at F.) Viscosity Gas Formed Index of Test Fluid Dosaee Index Damage N0. N0. (RXIO 100 130 '210 Orig. Irrad. Orig. Irrad. Orig. Irrad.Orig. Irrad. p.s.i. ml/ml. oil T mo Irradiated in glass containers, opento air 97".-- V-88 1.90 15.2 13. 6 8.85 7 3.38 2.95 105 64 123 8.8 98V-89 1. 90 63 49 9 31.4 19 0 9.13 7.2 125 112 203 7 65 99 V-90 1.90 166143 64.4 57 5 13. 5 11.3 78 60 2 8.4 100. V-91 1. 90 345 235 114 93 23.017. 5 91 86 269 7. 8 101. V-92 1. 90 304 252 109 96 20. 7 17.0 87 73 28.4 102 V-93 1. 90 340 304 112 105 18. 0 15. 7 48 28 248 8. 5 103V-94 1. 90 704 562 231 195 37.4 28. 6 79 303 8.0 104 V-95 1. 90 835 716234 210 30. 7 25. 5 51 28 280 8. 3

Irradiated in magnesium containers. under helium 105 V-88 93 15.2 8. 853. 38 105 empty 123 106 V-89 93 63 l 20. 7 31. 4 9. 13 40. 5 79 805 38203 47 107. V-90 93 166 1 45. 5 64. 4 13. 5 109 78 54 495 23 231 60 108-V-91 93 345 1 62. 8 114 23.0 148 91 94 805 38 269 43 109. V-92 101 304 l1, 105 20. 7 87 hi h 261 110. V-93 101 340 1 327 18. 0 1, 331 48 65 high248 360 111 V-94 101 704 1 121 37. 4 299 95 104 high 303 48 112 V-95 101Y 835 1 207 30. 7 398 51 124 699 31 280 138 113- V-96 99. 5 1, 378 77113 54 so id 114- VII-114 86 32. 0 1 399 1. 76 6. 24 196 139 6 128 I 261 Viscosity at 250 F.

drophobic finely divided silica obtained from E. I. Du

by National Lead Co., Baroid Sales Division, as Bentone 60 34 (believedto be dimethyl dioctadecyl' ammonium bentonite), the various gel-formingfinely-divided oxides, e.g., silica aerogels, silica hydrogels, andestersils, as described in Patents 2,711,393; 2,583,604; 2,260,625;

2,676,148, and 2,746,922. The gelling agents and com- 65 binationsthereof are used in amounts sufiicient to thicken the liquid mixture toa grease consistency. Normally such amounts range from 120% of the finalgrease or thickened oil compositions.

EXAMPLE VIII To portions of fluid composition of 10% poly(a-methylstyrene), 2.5% styrene-olefin copolymer (both described in earlierexamples), 5% didodecyl selenide, 0.1% 75 The following 50 pany. Theterm estersil as employed herein isconventionally employed in the art toind-icatea fine, freeflowing, hydrophobic silica powder obtained byesterification of free silanol groups (--SiOH) on the surface of thesilica particles with a monohydric alcohol (pp. 441, The CondensedChemical Dictionary, Reinhold Publishing Co.).

Grease Institute to indicate grease consistency, as determined' by'ASTMworked penetration. The-penetrations and dropping points aredeterminedbyASTM Test Designation D217-52T' and D566-42, respectively.

The Navy gear'wear test is carried out with small spiral bevel gears ofbrass and of steel with pitch diameters of 0.359 and 0.4769 inch,respectively, run together under a prescribed load. The powersou'rcedelivers a sinusoidal reciprocating motion of 3.14 amplitudeat 50 cyclesper minute. The gears are run in'on di(2-ethy1- hexyl) sebacate for 1500cycles under a five-pound load. After this time the weight loss must'nothave exceeded 2.0 mg. per 1000 cycles. The gears are then oper'ated for6000 cycles on the test lubricant at five-pound -load followedby anadditional 3000 cycles at a ten-pound load. The load is applied intorsion so that the gears are loaded against the helix. The gears arecleaned and weighed at each test interval. The criterion of the test isthe weight loss of the brass gear to the nearest 0.1 mg.

per 1000 cycles.

The NLGI Grade No. is the classificatior'l 5 adopted on October 2, 1939,by the National Lubricating 15 The four ball wear test was carried outas indicated in Example V but with the rotational speeds and jaw loadsindicated below.

Table VIII Added Agents, percent by Weight Test Nos.

Estersil. Lithium hydroxystearate. Carbon Black Granhite Molybdenumdlsulflde Lauryl phosphoric acid-.. NLGI Grade ASTM Worked PenetrationASTM Dropping Point Navy Gear Wear Test:

(a) 6,000 cycles at lbs., rug/cycle (b) 3,000 cycles at lbs., mg./cycleFour Ball Wear Test:

(a) Steel on Bronze, 800 r.p.m. 30 min; scar diam, mm.

at 2 lb. jaw load at 5 1b. jaw load (0) Steel on Steel, 800 rpm. 30 min;scar diam,

mm.,20lb.jawload EXAMPLE IX Some of the test greases from Example VIII,identified as test grease VIII-116 (corresponding to test grease 116 ofExample VIII), etc., and other grease compositions, described below,were irradiated. In tests 124 and 125, the greases were exposed, at C.in magnesium vessels sealed under helium, to the radiation sourcedescribed in Example IV. The same source was used to irradiate thegreases of tests 126-128, at 25 C. in magnesium vessels open to the air.The greases in tests 129-132 were exposed, at 25 C. in steel vesselsopen to the air, to the cobalt-60 source described in Example I. Thepenetration (both before and after irradiation) were calculated fromactual penetration obtained with a quarter-size cone. Test grease IX-129below was composed of 13.9% estersil (as described for Example VIII), 8%iodonaphthalene and the remainder the 250 average molecular weightalkylbenzene mixture used in fluid B of Example II. Test grease IX-l wascomposed of 10.9% of aluminum stearate and the remainder the 330- 340average molecular weight alkylbenzenes used in fluid F of Example III.Test grease IX-131 was composed of 13.1% of the same estersil, 8% ofiodonaphthalene and the remainder amylbiphenyl. Test grease IX-132 is acommercial aviation grease, NLGI, Grade 2, containing a lithium soapthickener and a mineral oil base.

exposed, at F. in a metal can open to air to 47 X 10 roentgens from theradiation source described in Example IV. The grease before and afterirradiation had the properties shown in following Table X:

Table X AS'IM Penetration AS'IM Dropping Point Unworked Worked F.)

(60 strokes) Before Irradiation 199 290 500+ After Irradiation 121 426500+ Table IX Test N0 124 125 126 127 128 129 130 131 132 Grease N0VIII-122 VIII-117 VIII-121 VIII-122 VIII-116 IX-129 IX-130 IX-131 IX-132ASTM worked Penetration at Dosage of RX1O None 233 290 366 233 307 240211 97 288 5.1- 160 281 340 an a 397 81 R 363 57.5- 393 61.5. 388 355ASTM Dropping Point at Dosage of RXIO None 500+ 500+ 500+ 500+ 450 500428 5.1 500+ 262 500 378 ot ct l dis- EXAMPLEX tron, where such organicfluids are unpr e edy Another grease composition was formulated with70.8% of the 330340 average molecular weight alkylposed in the proximityof neutronic reactors, the instant invention may likewise affordbeneficial results. Moreover, aside from neutronic reactors, thisprocedure may benzenes used in fluid F of Example III, 8.5% of the 7s beapplied to resist damage from the same types of deleterious radiation,especially neutrons and gamma rays, emitted from other conventionalradiation sources of same, such as radium-beryllium neutron sources, andnuclear reactions effected by means of Van de Graafigenerator-energizedlinear accelerators, and cyclotrons, and the like. Various additionalapplications of the hereinbefore-disclosed method will become apparentto those skilled in the art. It is therefore to be understood that allmatters contained in the above description and examples are illustrativeonly and do not limit the scope of the present invention.

We claim:

1. A nuclear radiation-resistant composition which is predominately amixture of a base oil which is adversely affected by nuclear radiationsselected from the group consisting of long-chain paraflinichydrocarbons, longchain paraflin substituted aromatic hydrocarbons,organic esters and polyethers and a radiation-resistant, liquid polymerof an alpha methyl styrene which polymer is soluble in said base oil andmore viscous than said base oil, said mixture being composed of 1-70% ofsaid polymer and the remainder said base oil.

2. The composition of claim 1 wherein said base oil consists ofalkylbenzenes having an average molecular weight of 200 to 350.

3. The composition of claim 1 wherein said base oil consists of organicesters of dicarboxylic acids and aliphatic alcohols having about 6 to 12carbon atoms in the molecule.

4. The composition of claim 1 which contains as an oxidation inhibitoran organic selenide.

5. A nuclear radiation-resistant liquid lubricant whose viscosity doesnot change substantially with continued exposure to nuclear radiation,which composition consists essentially of a mixture of aradiation-unstable oil of lubricating viscosity and selected from thegroup consisting of long-chain paraffinic hydrocarbons, long-chainparaflin substituted aromatic hvdrocarbons. organic esters andpolyethers and an oil-soluble radiation-resistant liquid polymer ofalpha methyl styrene, said mixture being composed of 170% of saidpolymer and the remainder said oil of lubricating viscosity, and a minorportion of a viscosity index improving acrylate ester polymer, whichtends to decrease in viscosity upon exposure to nuclear radiation, saidacrylate ester polymer being present in such amount to ofifset asubstantial part of the viscosity increase of the lubricant due to thetendency of said mixture of base oil and styrene polymer to increase inviscosity upon exposure to a nuclear radiation.

6. A liquid lubricant having a substantially reduced viscosity change inthe presence of nuclear radiation said lubricant consisting essentiallyof a mixture of alkylbenzenes and an a-methyl styrene polymer which issoluble in, and more viscous than, said alkylbenzenes, said mixture ofalkylbenzenes and methyl styrene polymer being composed of 1-17% of saidpolymer and the remainder of said alkylbenzenes, said mixture being inmajor proportion and tending to increase in viscosity upon exposure tonuclear radiation, and a viscosity index improving styrene-3 to 4 carbonatom olefin copolymer which tends to decrease in viscosity upon exposureto nuclear radiation, said copolymer being present in a small amountsufiicient to offset the viscosity increase of the lubricant due to thetendency of said mixture to increase in viscosity upon exposure tonuclear radiation.

7. The improved method for the lubrication of a system being subjectedto nuclear radiation, which comprises lubricating said system with aradiationfresistant liquid composed predominantly of a mixture of alubricating oil selected from the group consisting of long i chainparafiinic hydrocarbons, long-chain parafiin substituted aromatichydrocarbons, organic esters and polyethers which substantially increasein viscosity upon exposure to nuclear radiations and an oil-solubleradiation-resistant, liquid polymer of alpha-methyl styrene in an amountsufiicient to inhibit said viscosity increase of the lubricating oil.

8. A radiation-resistant lubricating grease composition composedpredominately of liquid mixture of a base oil selected from the groupconsisting of long-chain paraffinic hydrocarbons, long-chain parafiinsubstituted aromatic hydrocarbons, organic esters and polyethers and anoilsoluble, radiation-resistant, liquid polymer of alphamethyl styrene,said mixture being composed of 1-70% of said polymer and the remainderof said base oil, and a small amount, suflicient to thickensubstantially said liquid mixture to a grease consistency, of agel-forming finely-divided silica.

9. The lubricating grease composition of claim 8 wherein the gellingagent is an estersil.

10. The lubricating grease composition of claim 8, wherein the base oilis alkylbenzene of an average molecular weight from 200-350.

11. The lubricating grease composition of claim 8, to which has beenadded a small amount of an iodosubstituted aromatic compound.

12. A liquid lubricant with a substantially reduced tendency toviscosity change in the presence of nuclear radiation, said lubricantconsisting essentially of a major proportion of a mixture composed of ahydrocarbon lubricating oil and 170% of an oil-soluble liquid a-methylstyrene polymer, said mixture tending to increase in viscosity uponexposure to nuclear radiation, and a minor proportion of a viscosityindex improving olefin polymer produced from olefins having chainlengths of 3 to 4 carbon atoms and which tends to decrease in viscosityupon exposure to nuclear radiation, said olefin polymer being present ina small amount sufiicient to offset the viscosity increase of thelubricant due to the tendency of said mixture to increase in viscosityupon exposure to nuclear radiation.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Wall: Elfects of Atomic Radiation on Polymers," ModernPlastics, July 1953, vol. 30, No. 11, pages 111, 112, 114, 116.

Charlesby: How Radiation Afiects Long-Chain Polymers, Nucleonics, June1954, vol. 12, No. 6.

Mincher: Radiation Damage to Various Non-Metallic, 1

Materials, A.E.C. Kapl-731, April 2, 1952; declassified February 15,1955; pages 3-8, 12, 15, 16, 19 and 48; I

Knolls Atomic Power Lab., GE. 00., Schenectady, N.Y.

1. A NUCLEAR RADIATION-RESISTANT COMPOSITION WHICH IS PREDOMINATELY AMIXTURE OF A BASE OIL WHICH IS ADVERSELY AFFECTED BY NUCLEAR RADIATIONSSELECTED FROM THE GROUP CONSISTING OF LONG-CHAIN PARAFFINICHYDROCARBONS, LONGCHAIN PARAFFIN SUBSTITUTED AROMATIC HYDROCARBONS,ORGANIC ESTERS AND POLYETHERS AND A RATION-RESISTANT, LIQUOR POLYMER OFAN ALPHA METHYL STYRENE WHICH POLYMER IS SOLUBLE IN SAID BASE OIL ANDMORE VISCOUS THAN SAID BASE OIL, SAID MIXTURE BEING COMPOSED OF 1-70% OFSAID POLYMER AND THE REMAINDER SAID BASE OIL.